X-ray cathode shield



'ug- 1, 1933. N. H. STEWART 1,920,605

' X-RAY CATHODE SHIELD Filed Deo. 1, 1931 INVENTO MfS/ 50N fr.

BYMQ:

ATTORNE 10-Vsprng members directedtowards tle anode'.4 between the` anode and theedges of the resilient 65 25 or hemisphericalfcontour-,and'having at its other vices.r

40 and within the inner sidewalls ofjthe metallic. Y Frig 3 represtsma'mdicfin flpigl'l, h 9'5 v PatentedAug. 1, 1933 e y 'i d l i {1191205606}di r UNITED STATES PATENT `Westinghouse Lamp Company, a Corporation Y `of Pennsylvania i Y Y f V Applicationnecessari,1931. serialNo. 578,243 v n vcklaims; (C1, 25o-35) f `This invention relates to electricaldischarge his-application heretofore identied disclosesanl i. `devices and more particularly todevices of this improvement over the `Ulrey resilient members" Y character vemployed for` the production lof Xe. and substitutes therefor a plurality of spaced re'-A rays and commonly'termed Xfray tubes. in its silientplatesof about the same orderof thick- 5- more specic aspect Athe invention Yis directed ness as the resilientbearing portions of the Ul- 60 towards the preventionv of undesirableelectrical lrey cylindrical spring" sleeves'.` discharges and especially thoseoccurring or hayl t sometimesfhas been'iound'rthat vvhen "a" ing a high tendency to occur at the edges of the voltage is applied between the anode and-the X-ray screen supporting and-'shock absorbing cathode that an electrical discharge takesplacei- Since the period"of,vRoentgensfdiscovery, Xe supporting, and` shockfabsorb'ingy means', surraytubesof variable designs and sizes have been rounding the screen and.v 'facing said1 anode. rather 'extensively `employed Linsundry and dif- This may'be inifthe nature of, a 'corona effect ferent fields. One type offXra`y tube design around these edges of saidresilientnieans orvr a 15- Which I shallemploy merely 'as an illustration spark over therebetweenand the anode; 70 'so that the benefits ofkmyinvention'may be..A This invention'has beendevised to eliminate made clearly apparent is that described in U. S'. or at least greatlyminimize this'obviously un- Patent 1,715,152 granted to C. TwUlrey 3 et al. desirablevefiect and briefly4 stated comprises proon May 28, 1929 and that describedinthe patviding afmeaiismfor shielding the edge'sfof'kfthe l 2o ent application of A. C. 'Blakemam Serial No. resilient supporting and shocl absorbing'means 75 560,738,1led Sept. 2, 1931 and assigned. tothe from the anode.` f l l 'f same assignee as'the present inv`ention-v` f y V Anobject of myinvention is to Aprovide means The'X-ray tube 'generally' comprises acyln'- forthe elimination of some'ofthe undesirable d rcal envelope having one of itsends of bulbous electrical discharges in electrical discharge des` v 1- I' `so end a reentrant-tube' Whose diameter is substan- Another object vo f iriy'ir'ivention-` is to `provide tially less than the'lcorresponding dimension of an X-ray 4tubeof' rugged mechanical and" elecfv Vthe envelope. Along about the middle third trical design. s length of the envelope' is a second reentrant MAnoth'er object ot my `invention is'to provide 30 tube, with one of vits ends fusedly secured to the means for the., elimination offelec'trical dis. '85 l envelope. Disposed above the'free end of said` charges'zat vthe edges of the s creenhsupporting y second reentrant tube is a suspended metallic and shock absorbingfmembers'ofanX-ray tube'. screen, housing a' cathode Yand having its outer Fig;` 1 represents` a ,fragmentary View with "Surfae SDaGGd from the' inner Wall of 'the enn someV of the parts shown in elevation and others 'f 35 velope. `'Iheinner endof thefirst mentionedrein Section of anxqa'y tube embodying my in; 90` entrant tube has firmly sealedthereto avnietallic Ven'jon` s g' 1 sleeve adapted to support an anode. The anode, Fig'. i2 represents a `cross sectional viewhtaken being of such lengthwise and cross sectional dion line n n of Fig. 1 inthe directio of `the mensionsthat its loaded f-ree end is spacedl from arr0Ws ly screen, has its` outer wall ora substantial por-` Fig, 4 represents "a crosssectional vieu'f'talre-nl iln'thefeof Surrounded by and .spadffom the 4on une vIv-Iv .of rig.v a inihedirectim ofthe inner vvall of the'second' reentrant tube: f y arows. ,I j'. .Y 'A

4. Nides;arrears.i@sans:are my. s g

ray 'tube of thisV design were enhanced by pro- Ventlon' .applied 1.30 an X-raytube'ofthggenf V l viding supporting and 4shockabsorbing means ml-typedlsclosed mi-thflUlfey'etalpatent and for the anode and cathode'screen. As shown theilakema'n applicatlon herembeforefident'. therein the anode and the cathode are sur` edf I 'do not mean t0 be limited thereby butf 5e rounded by and secured to slotted resilientcolmelfelyvemploy these; constructionsf as ,convent 105 lars o1' sleeves respectively bearing against the ent means 0f llllSTaOn- --MOIGOVVerfSiYnce the l lsecond reentrant -tube andthe envelope. The 10We1 Gnd fan X-ray tube embodying a reen-V resilient frictional bearing portions of these trant'tlb With ali anode Supportingv land Shock e e sleeves areV relatively thin andare or the order absorbing means is notessential tothe illustra-- of about .020 inch in thickness.' VBlakcman in tion of my inventionpl Ash'all describe'butvthe 110 upper portion'of an X-ray tube embodying my invention.

In both Figs. 1 and 3 there, is illustrated the upper portion of an Xray tube, embodying my invention, which comprises a gas tight lenvelope 10 consistingof a body .portion 11 anda hernispherical or bulbous upper end 12. At the up'- per end of the body portion 11 and in close proximity of the hemispherical portion 12 isa nickel-iron screen 13 housing a cathode (not shown) and the target end of an anode 14 and adapted to screen out undesirable X-rays.v The` cathode is supplied with electrical current by means of a plurality of conductors hermetically sealed to the envelope 10,.one of which is shown as at 15. Besides serving as electrical conducting means, these conductors 15 act to Vsupport the kmetallic screen 13. n

So that the tube may be able to withstand shocks without danger of breaking during the normal commercial manipulations, transportation and'operation, thereare provided resilient means between the outer surface of' the screen 13 and the inner wall of the envelope l() all shown by both Ulrey et al. and Blakeman.,

. extending from the upper edge of each plate is an ear 19 having suitably sized openings .there through. v'Ihescreen 13 has a plurality of spaced depressions 21 adapted to receive the nipples 18 ofthe plates 16, andthe uper end of the envelope above the screen has a plurality of nipples 22 on the inner surface thereof adapted to t in theopening of the ears. 19.

As shown" the plates V16 are mounte'dbetween the outerrsurface of the metallic screen 13 and the in ner surface 'of the envelope'lO. The nip- 'y' ples on the plates and envelope fit,V snuglyin .the depressions21 and the openings-lerespec .tively with the plates lflexed inwardly towards the `metallic screen and `having-a major portion thereof bearing 'against the inner wall vof the envelope and` the edges of the marginal portions thereof bearing against the metallic'screen When a suflicientlyhigh voltageA is vapplied between the electrode terminals of a' tube of this construction, it was observed that there sometimes. occurred an electrical -r discharge at the end 24 of the Vresilientmeans 16 facing the This electrical Adischarge manifested itself in the nature of a corona effect Varoundtheseedges and ,sometimesV in rthe nature of a spark over between these edges and the anode or the anode supporting sleeve (notshown). Y

VThese phenomena iffthey persisted'oftentimes causes an electrical charge to build up on some kportion of the glass -which 'eventually'.causesfa rupture thereof.'

According torny invention, in orderr to avoid or to at least materially minimizethese liabilities, I provide an inexpensivemeans which may .be readily assembled; with the screen and which yfunctions in the nature of a shieldto :decrease the potential gradient at the edge f.of the resilientplates to minimize the tendency of an electrical discharge occurring'at these edges. This shielding means may be of any suitable design and as shown in Fig. 1 it comprises a vsplit ring.

25 of a resilient refractory material such as resilient molybdenum or the like measuring about .006 inch in thickness. `The screen 13 has a circumferential slot or recess 26 of appropriate dimensions in the outer surface thereof so that the ring 25 may be readily mounted K thereon with the outer surface of the lower edge .thereof being positioned inwardly of the outer surface of the screen 13 or preferably -Aiiush Y therewith.

The ring 25 when mounted consists essentially of a cylindrical lower portion 27 having integrally therewith an upwardly and outwardly .extending curved. shoulder 28 .of a relatively large radius as compared to the lower edges of with the upper edgefof said shoulder and eX- tending upwardly therefrom. This ring 25maybe .readily manufactured by merely stamping ,A the plate 16 and a slotted cylinder 29 integral rectangular blank ofn molybdenum fof,Y appropriate dimensions to provide; an v. offset V.portion 27, a curved shoulder 28 integral therewith and a slotted.. portion 29 integral with and extending from one edge of the shoulder.

. Thereafter the ,ring 25may be assembled with` `the screen 13 toprotect the edges ofthe plates 16 by wrapping the ringharound thescreen 13,

'with the offset portion 27 of the vring located within the circumferential slot or recess 26, with the shoulder 28 'curvedvr aroundk the edges of the plates 16 and the slotted upper .portion 29 encircling and Ybearing against the lower yportion of theplates 16.

The ring 25 isl secured to the screenl byvvspot -welding vor by means of appropriate `pins or screws through the offset portion 27 thereof and the screen n13. acter, it is'apparent that the edges ofthe plates .16 ,are shielded fromthe anode and that the slotted portion 29 of thering 25 bears against the outer surface of the lower portionsof the plates 16 andfthe inner wall ofthe envelope 10 to yaid inxsupporting the. screen 13 and in dis-l tributing and absorbing anygshocks on the envelope.

A modification Fig. 1 is'that Yillustrated in Fig. v3. `As shown in Fig. 3 an alternative meansthat'gmay be employed as a shielding meansfor the lower edges ofthe plates 16 may 'comprise a split spring ring 3i) of resilientmolybdenum measuringabout .066V inch in thickness orany other suitable material of appropriate thickness. The screenA 13 has a circumferential slot 31 on fthe outer surface thereof, Ylocated below the edges of the plates 16 and adapted to accommodate a portion of the splitI springring 30. This split springringA 30`may comprise a generally cylindricalV portion, 32 yhaving an outwardly curved shoulder 33 integral therewith and ofv a relatively greater', rradius than thatfof theA lower edges of the plates 16, andan `inwardly directed flange 34 integral with the shoulder 33` and ap- In-a construction of this charlio of my inventionf as shown in Y proximately normal to the cylindrical portion 32.

A small `rmertionof one `extremity of the splitv spring ring '3e is offset slightly inwardly asv at35 d 1,92o,eoe the shoulder 33 curved around the edges of the plates 16 and the flange 34' extending into the circumferential recess or slot 31.

In order to assurea rugged flexible assembly and to eliminate the necessity of, welding or the use'of pins, there' is provided a split wire ring 36 of appropriate dimensions which is located in the slot v31y and bears against the upperedge of the slot 31 and against'the upper surface of the ange 34.

This split spring ring Lmay AbeV readilyv mounted on the screen 13'by first placing the wire ring 36 in the circumferential slot 31. Thereafter the split spring ring 30 is placed therearound with the flange y34 located vin the .slot 31 and abutting` against the lower limit of this slot and the wire ring 3 6 and having its r ends overlapping as at 35. The cylindrical portion 32 thereof bearsagainst the youter surface of the'lower portions of the plates16 and when assembled with the envelope this cylindrical portion 32 bears against both the outer surfaceA of theplates 16 and the inner surface of the wall of the envelope 10. VIn a construction of this character it is apparent that like the construction in Fig. l, the edges of the plates' 16 are shielded from `the anode and the cylindricalzpor- I Y tion 32 of the shield aids in supporting the tively thin supporting means bearing against the A outer surface of said screen and againstthe inner wall of the envelope, and means associated with said screen and shieldingfrom said anodeone edge of said supporting 'meansfacingfsaid Y anode to lower the potential gradient at the edge of said supporting means facing said anode.

2. An Y-ray tube including anv envelope with a cathode, an anode and a screen therein, said screen housing the. cathode, relatively thin resilient supporting means bearing against the outer surface of the screen and the inner surface ofthe envelope and means on said screen shield-` ing the lower edge of said supporting means from the anode, said means having a portion thereof whose radius of curvature is greater than that of said lower edge. 3. An X-ray tube including an envelope with a cathode, an anode, and a screen therein, said screen housing said cathode, relatively thin `supporting means bearing against theouter surfaceA said slot.

V6; An X-ray tube including an envelope with* of the screen and against the vinner; surface Vof the envelope, one of the edges vof said supporting means facing the anode and 'acsplit Yring located between said Asereenandlthe envelope, with a portion thereof shielding said edge from the'anode. v v

' 4. An AX-vray tube including an envelope with" la cathode,` ananode, and-a kscreen therein, said Screeny housing the cathode, relatively 'thin supporting means bearing against the outer surface thereof and the `inner Vwall of the envelope, one.

of ythe edges of vsaid supportingfmeans Vfacing the anode, a slot in` thelowerfportion of the screen adjacent said edge, and ashield surroundi I ing the said edge and having a portionthereof located in said slot.A f l 5.- An X- ray tube including an envelope with a cathode, an-anode anda screen therein, said` screen `housing the cathode,l relativelyv thin supporting means ,bearing against the Youter surface thereof and the inner wall of the envelope, one of the edges of said supporting meansffacingthe C adjacent said edge, and a split ring having a portion thereof bearing against the outer surface of said supporting means and shielding said edge from the anode andanother portior'rlocated in a cathode, an anode and a screen therein, said Ascreen housing the cathode, relatively :thin supporting.v means bearing against` the outer surface anode, va slot in the lower-'portionof 'said screen f thereof and against the inner Wall of said enve` lope, one of the edges of Vsaid supportingmeansv facing the anode, aslot inthe lower portion of said screen adjacent said edge, and means having a portion thereof bearing against the outer surface of the lower rportion of said supporting Vmeans and shielding said lower. edge Vfrom the anode and V.having another portion thereof located in said slot. I

"7.r An X-ray tubeincluding`anenvelope Awith t a cathode, an lanode anda screen therein, said screen housing the cathode, relatively thin sup` 120 porting means bearing` against the outer `surface thereof and against the inner'surface of ing means facing thel anode, a slot in the lower portion of the screen adjacentisaid edge and means 'surroundingthe lower portion of said vsaid envelope, one of the edges ,of said support# supporting means, vsaid last named means having a curved portion surroundingsaidedge, the ra-4 dius of curvature of said curved portion being Ygreater than that of said edge,said lastrnamed means having `a portion thereof located in'is'aid slot. y NELSON H. STEWART, 

